JP2004-67070A discloses a driving operation assisting system, which transmits information related to an environment surrounding a vehicle to an operator by deceleration, as well as by varying a reaction force applied to an accelerator pedal based on different values of risk potential. This type of system increases the amount of deceleration and accelerator pedal reaction force in view of an increase in risk potential. However, the increased accelerator pedal reaction force and vehicle deceleration impair the response of the vehicle to a proper acceleration intended by the operator. Accordingly, there is a need for a driving operation assisting system that transmits information related to an environment surrounding the vehicle without impairing an intended acceleration by the operator.